Exercise may take several forms including aerobic or cardiovascular, strength training, flexibility training, and balance training. With particular regard to strength training, two common forms include free weights and exercise machines. In the case of weight training exercise machines, it is common for the machines to include a user interfacing portion such as a graspable bar or handle, a foot press, a leg pad, or other interface. The interface may be connected to a cable or series of cables that may pass through one or a series of pulleys and be connected to one or more weight plates. As a user exercises, the one or more weight plates may be lifted from a resting location.
A common exercise machine may include a weight stack where each plate in the stack is adapted to slide along two guide rods. The cable in these machines may be attached to a selecting probe passing through the weight stack and having a plurality of holes adapted to align with holes in each of the plates in the stack. A selection pin may be inserted into one of the plurality of holes via a hole in a respective weight plate thereby engaging the selected plate, and all of the plates above it, with the selecting probe. Friction may be developed between the selection pin and the weight plates due to the weight of the plates pressing against the surface of the pin. Friction may also be developed between the pin and the selection probe due to the weight of the plates being supported on the pin and all of said weight bearing on the selected hole in the selection probe. As such, the selection pin may be securely positioned in the one or more weights being lifted as soon as the weights are lifted from their resting location and forces come to bear on the selection pin.